Ferrites for microwave applications



April 25, 1961 E. ALBERS-SCHOENBERG 2,981,688

FERRITES FOR MICROWAVE APPLICATIONS Filed May 27, 1960 United StatesPatent'Oi'ice 22 3381: R CRO AV IC THPNS Albers schoenberg, RetlfieldVillage, Metuchen,

tele ram t efiect is: die we teraction of:

;N.'.I., assign r, by mesne assignments, Steatite Re- Search C6 fDelaware Filed Mam, 1 9 66, ser No. 32,387 Claims. (01. Zea-62.5

. mre t;su ate of ber 28,-19 l8, also abandoned. In application SerialNo.

67,752 an unusual type of fe'rrite material is disclosed; Whereasltheordinary ferrite has a formula of xi/rom o,

and inwhich czy'is approximately l:1, tlie ferrites disclosed in saidapplication Serial No. 67,752 havewan xzy ratio which is between 1.221and 31-1 and preferably between ,1.6:1 and 2:1. These ferrites utilize'MgOas the essential bivalent oxide. w Application, Serial No. 352,205disc10ses that a certain group of ferrites disclosed in U.S. applicationSerial No; 67,752 having an xzy ratio of 1.2:1 to 3:1, have unusualproperties making them particularly suitable as gyrator element whichhas very low losses'insuch ap:

plications.

Among other objects of the invention is to provide a ferromagneticferrite having low dielectric losses especially useful for microwaveapplications.

Another object of the invention is to provide a new connection with theaccompanying drawing in which thesingle figure is a perspective viewpartly in cross section of" a circuitinventiomt h H Recently, thegyrator elements, referred to above,*com

em em the t s -eta 9 h prising wave guides including ferrite coresy haveevolved as new circuit elements for microwave frequencies. Such gyratorelements are useful for phase' changer s,modulators and switches, forexample. I: H

This type of new; circuitelementis a uniqueYdevice, since it violatesthe law of reciprocity; that is itdoes not have similar properties inboth directions ,equally The planeof polarization of microwavepropagation can be changedas the wave passes through the ferrite whichis magnetized with a steady field. I This device can proper; 135 be.called a ferrite gyrator element! The ferrite. core has been named aFaraday plate. The actual effect upon (1) The spinning electrons whichwill precess about a force not'parallel to their axis of spin (similarto a y p 1 I I (2) .A steady magnetic, field parallel to the directionof propagation which acts as the aligning forceon the gyroscopicspinning electrons inthe ferrite,

(3) Circularly polarized waves in the wave guide which are propagatedthrough the ferrite.

Actually, circularly polarized waves are not necessary since anylinearly polarized wave can be considered as the resultant of twocircularly polarized components of equal amplitudes which are rotatingin opposite directions with equal angular velocities. Thus, onedirection of circular polarization'will be in the same direction as theprecession of the elemental electron gyroscope and the other directionof circular. polarizationwill be in the opposite direction to thatfoftheprecession. It is evident that one component of circular polarizationwhich has the same sense of circular direction as the precession of theelemental electron gyroscope in the ferrite will be rotated more thanthe normal amount due to angular velocities, While the other circularlypolarized wave of the opposite direction will be rotated only the inormal amount, or less, than that, due, to its angular in which Mrepresents one or more bivalent metal oxides velocity. Thus, at the exitend of the ferrite, there will be a relative phase shift between hothcircularly polarized components. When these are combined again into thelinearly polarized wave, the plane of polarizationofthe latter is shifted ,with res pect to the plane of polarization before, it entered theferrite. Another way of looking at phenomenon is to consider it as arelae change bf the velocities of propagation of the/circularlypolarized waves. n a If very much attenuation of both circularlypolarized waves occurs due to the loss characteristic of the ferrite,

thenfits efficiency as a transparent medium is poof. If the'twocircularly polarized waves which emerge from the ferrite areattenuatedunequally, then an elliptically polarized wave will result; n

' Difierent ferrites vary as to their attenuation proper ties "(or losscharacteristics), ellipticity (or unequal 'attenuation of the twocircularlypolarizedwaves), and rotation. In addition, as onewouldexpect, these propw erties" vary -as afunc'tion of the steady magneticfield.

Also,fthere is a resonance point present whenthe precessionfrequency oftheclernental electron gyroscopes coincides witli that of the microwavefrequency. This point is characterizedby complete absorption of theinteracting circularly-polarizedwave, and thus, very high losses. Lossesina Faraday plate or'ferrite cores of such devices'may comprisedielectric losses, magnetic losses or rnay'bedu'e to some other unknownquality'of the core; For example, it is believed that the low losses andefiec tiveness of the core of thepresentinvention are not only dueimitsmagneticand dieleotricproperties but that they are in. some. wayassociatedwith thepresence of more than one crystalline phase in thematerial due to the low proportion of Fe O with respect to the bivalentmetal oxides. l 7 3 The ferri tes employed in the gyrato'r. of thisinvention not only have low losses but combine withthis property afairly high rotation. These two properties are both dc sirable in aFaraday plate.

The ferrrtes f the gyr ator element of this invention comprisecompositions which areessentially of the for inula x(MgO, MO)yFe O inwhich the MO represents a heavy metal oxide which is less than 10%by'weight of theentire composition (with the exception' of MnO which maybe added in amounts up to 20% of "the corh n Patented Apr. 196 1 The MOmay be entirely absent and may be MnO, ZnO,

CdO, CuO, NiO or any similar bivalent oxide. When oxide fluxes until atotal of 20% of flux is obtained although with no more than 10% of theother bivalent oxide fluxes.

. Ferrites within the limits specified but containing over 55 molpercent of MgO are very satisfactory since they have a lowsusceptibility to compositional variations and may therefore be madewith very. uniform properties. Increasing the MgO content to 55 molpercentreduces the maximum allowable iron oxide content to 44 molpercent and the maximum amount of MnO to 22 mol percent.

The properties of such ferromagnetic bodies which probably relate totheir application in gyrator elements are as follows:.

(a) Initial permeability 10-40 at 1 me.

(b) Saturation magnetization, B of approximately 1500 'gausses.

(0) Dielectric constant of about 8 to 20.

(:1) Low magnetic losses at 1 me.

(e) Relatively low dielectric losses, tan 6, of about .05 at 1 mo. andabout .001 at l0 c.p.s.

The dielectric constant of such bodies does not substantially change upto 10,000 mcs. However, the dielectric constant at these frequencies isdiflicult to measure with accuracy. The initial permeability at 10,000mcs. may be as low as unity. The magnetic losses at 10,000 mcs. varysomewhat, but are, at least,

. Magnesium oxi e Specific resistance 0.8)(10' ohm Power factor, tan 6170x10 Initial permeability f.. (Approx) 30. Dielectric constant About10.

At 10,000 mcs. the initial permeability is about 1.0.

EXAMPLE 2 A ferrite core is made of the following composition Partsbyweight 2s Magnesium fluoride i 3 Manganese dioxide 6 Iron oxide 66Approximate ratio of x:y=1.8:1. Firing temperature =1390 C.

This body has lower magnetic losses at 10,000 mes.

than the body of Example 1 and represents an improvement over such bodyin this respect.

When these bodies are inserted in the device of the drawing as the plate20 in diameter of .6 cm. f.c. a gyr'ator element having exceptionallylow losses and good performance is produced. The measurements ofrotation were obtained on samples of 1 inch or 2.54 cm. length. Suchcircuit elements are useful for. one-way transmitting devices, forexample, and since the rotation of the wave may be controlled by anexternal source of the magnetizing current they may also be used inelectrically controlled attenuators, modulators and microwave switches.

The following tables give the essential features of further examples.

by one order of magnitude smaller than that of other ordinary ferritematerials.

The device shown in the drawing has a first rectangular wave guide 10and a second rectangular wave guide 11 connected by a circular tube 12in which the Faraday plate or ferrite 20 is placed. A magnetizing coil21 surrounds the central portion of the circular tube 12 to magnetizethe ferrite plate 20. Depending on the thickness of the plate or lengthof the ferrite 20, the amount of magnetization, etc., the wave in guide1 1 will be rotated a certain number of degrees, in a clockwisedirection, 90, for example. 'If any wave of the same frequency, etc., ispassed from guide 11 through plate 20 and then to guide 10 this wavewill be rotated 90 by Plate 20 'but if passed in a counter directionwill not be rotated in the opposite direction (as would be expected bythe law of reciprocity) but in the same direction. Any reflected wavewould therefore be 180 out of phase with respect to the original wave.In the device shown, the central circular tube 12 is about the diameterof an ordinary cigarette.

EXAMPLE 1 A ferrite core is made by grinding, mixing and firing acomposition of the following ingredients in the propor tions disclosed:

' Parts by weight Oalcined magnesite 21 Magnesium fluoride 1 Manganesedioxide 6 Zinc oxide 1 Iron oxidelFe o 71 EXAMPLES 3-6 Example 3 Example4 Example 5 Example 6 7 Mol wt. Mol Wt. Mol Wt. Mol wt. -Per- Per- Per-Per- Per- Per Per- Percent cent cent cent cent cent cent .cent

M30 58 26. 3 58 28. 1 58 29. 1 58 27. 2 MnO 2 1. 9+ 10 10. 5 14 16. 2 55. 1 N10 1 9 F010: 40 71. 8 32 61. 5 28 55. 7 36 66. 9 Rotation, 2.54cm.

or 1 inch, degrees 202 176 162 212 Losses Low Low Low Low.

I But sllghtly hlgher than 101. Examples 3-5.

V EXAMPLES 7-11 Ex. 7, Ex. 8, Ex. 9, Ex. 10, Ex. 11, Wt. Per- Wt. Per-Wt. Per- Wt. Per- Wt.'Percent cent cent cent cent MgO 25 30 30.5 MgO V44 48 MgF- 3 8 .01 0 6 M11104.H|O 4. 5 4. 6 FerOr 66 51. 5 61 47. 6 69.6 M01 ratio 1.8 1. 8 2. 3 2.3 1. 76

Mg0+MO FerO:

Examples 7 and 8 produce substantially the identical composition afterfiring and similarly Examples 9 and 10 produce the same end product.Example 11 illustrates a body prepared without additional flux. In orderto obtain a satisfactory product from this composition the materials aremixed,'fired at around 1400 C. and-thereafter refired several times. I

Examples7 and 8 have low losses and a rotation of approximately 220 perinch.

Examples 9 and 10 have low losses and a rotation of approximately 180per inch.

Example 11 has low losses and a rotation of approximately per inch.

When the term low losses" is employed it means that the losses are below1.0 decibel, for example.

The features and principles underlying the invention described above inconnection with specific exemplifications will suggest to those skilledin the art many other modifications thereof. It is accordingly desiredthat the appended claims shall not be limited to any specific featuresand details shown and described in connection with the exemplificationsthereof.

I claim:

1. A ferromagnetic ferrite consisting essentially of a composition ofthe general formula x(MgO, MnO, Mo Fe,o,

in which MO consists of at least one bivalent metal oxide selected fromthe group consisting of ZnO, Q and NiO, in which xzy is between 1.2:1and 3:1, the total amount of MO being less than 10% by weight of theentire composition, the amount of MnO being at least 1% and no more thanby weight of said composition, and the total amount of MO and MnO beingno more than 20% by weight of said composition, said ferrite having lowdielectric losses, tan 6, of no more than about 0.05 at 1 mo. and of nomore than about 0.001 at 10 c.p.s.

2. The ferrite of claim 1 in which the ratio of x:y is between 1.6:1 and3:1.

3. A ferromagnetic ferrite consisting essentially of a composition ofthe general formula x(MgO, MnO) .yFe O in which any is between 1.2:1 and3:1, the total amount of manganese oxide being between 1 and 20% byweight of the entire composition, said ferrite having low dielectriclosses, tan 6, of no more than about 0.05 at 1 me. and of no more thanabout 0.001 at 10 c.p.s.

4. In a ferrite gyrator, a Faraday plate consisting essentially of aferromagnetic plate of the composition of claim 3.

5. A fired, shaped ferrite body having low dielectric losses, tan 6, ofno more than about 0.05 at 1 me. and of no more than about 0.001 at 10c.p.s., formed by firing at a temperature of about 1390" 0., about 25parts by weight of MgO, about 3 parts by weight of magnesium fluoride,about 6 parts by weight of manganese oxide calculated as M110, and about66 parts by weight of ferric oxide.

References Cited in the file of this patent UNITED STATES PATENTS2,565,861 Leverenz et a1. Aug. 28, 1951 2,576,456 Harvey Nov. 27, 19512,640,813 Berge June 2, 1953 2,644,930 Luhrs et al. July 7, 19532,715,109 AlbersSchoenberg Aug. 9, 1955 2,719,274 Luhrs Sept. 27, 19552,745,069 Hewitt May 8, 1956 2,748,353 Hogan May 29, 1956 2,877,183Eckert Mar. 10, 1959 2,886,530 Greger May 12, 1959 FOREIGN PATENTS697,219 Great Britain Sept. 16, 1953 735,375 Great Britain Aug. 17, 1955

1. A FERROMAGNETIC FERRITE CONSISTING ESSENTIALLY COMPOSITION OF THEGENERAL FORMULA